The present invention relates to improvements in the field of work piece holding devices for machines. More specifically, the present invention relates to a multi-element vacuum hold down device which contains upper and lower dressable surfaces and a flexible vacuum transmission web in between the multiple elements and which is useful in supportably working thinner materials, especially for downward beveling grinding forces without failure or with extremely reduced incidence of failure.
In many instances, it is necessary to locate, position and support a work piece which is to be milled, sanded, ground, etc. The precision and stability of the positional device is important, as is the ability to re-position the positional device. Positive location of work pieces which are relatively thick are described in U.S. Pat. No. 6,186,567 to John Blick entitled xe2x80x9cLocator and Hold Down system for a Machinexe2x80x9d which describes an integrated system for using multiple holders. A system for positive location and support of thin work pieces are described in U.S. Pat. No. 6,286,822 to John Blick entitled xe2x80x9cMACHINABLE SUPPORTS FOR CLOSE TOLERANCE EDGE SUPPORTxe2x80x9d and describes an integrated system for using multiple separately locatable holders where each holder has a base of sufficient dimension to both support and allow a user integrated placement of each separate holder. Pre-selected variations on shape degree of rigid spaced multiplicity were illustrated.
U.S. Pat. No. 5,433,657 to Luigi Bovone issued on Jul. 11, 2001 and entitled xe2x80x9cDEVICE FOR FIXING AND MAINTAINING SHAPEABLE GLASS PLATES IN POSITION DURING THEIR MACHININGxe2x80x9d discloses a rigidly pivotable series of fixed suction support elements having upper and lower vacuum areas for fixture to a work piece and a work table, respectively. However, the relationship between the suction support elements is based upon a complex hinge arrangement with machined passages in both the elements and the hinge portions. This arrangement is expensive and requires precision measurements both to make absolutely certain that the upper and lower vacuum support element are flush to the floor and work piece surface, as well as to insure that the hinge clearance is so closely tolleranced as to prevent undue vacuum degradation from leakage into the device.
The device of Bovone is heavy, bulky and difficult to place precisely about a work piece. Further, the Bovone device is not dressable to enable a greater precision of formation of the sealing and working height. Bovone recites xe2x80x9csuckersxe2x80x9d 11 which have no other further specification. The Bovone reference appears to indicate that xe2x80x9csuckersxe2x80x9d are metal structures. Thus height is controlled, but vacuum is not. Any nick on the xe2x80x9csuckersxe2x80x9d will cause further loss of vacuum. As a result, the structure of Bovone would have to be treated especially gently during handling.
Another problem with Bovone relates to the relatively rigid hinging between his support elements. Any twisting of the Bovone assembly, especially during handling could cause the entire series of supports to xe2x80x9cbindxe2x80x9d. Where one end of the supports was angled with respect to the others, or where the hinge axis was shifted through mishandling, the angularity of the individual support elements could be forcibly mis-aligned as dictated by the tight hinge relationship between the individual support elements.
What is therefore needed is a support specially formulated to closely support a thin work piece near its edge, and which provides a series of independent vacuum support elements, which is precision dressable, and which can provide even, secure support to a work piece.
The devices and systems of the present invention encompass the provision of a plurality of spaced apart supports specially designed to closely support a work piece immediately adjacent the edge being worked, ground or polished, but especially an edge which is being beveled or some other type of material process where downward force is applied to the edge of the work piece. The top and bottom surfaces of the supports are machineable in place on the working table to insure that all are brought to exactly the same height to prevent adjacent supports from creating uneven support and adjacent shear forces. Adjacent shear forced are also eliminated by the use of a polymeric interconnections used to both generally contribute to the spacing and to transmit the vacuum in a distributed manner among the individual support units.
The top and bottom members of the supports are a hardened rubber, or any other suitable machinable material which will not enable the work piece to displace significantly downwardly upon the application of vacuum but which will provide a vacuum downward force from the work piece to the support and from the individual supports to the work table surface.
The hardened rubber top of the edge hold down are machinable without losing the ability to act as a vacuum hold down. Such machinability is often referred to as xe2x80x9cdressabilityxe2x80x9d and enables significant advantages along with the fact that the top and bottom of the individual supports are selectively operable.
A given set of interconnected supports can a selective vacuum applied to hold the sit of interconnected supports to the work table. The upper surfaces can be dressed. The same set of interconnected supports can be turned over with the now bottom ends of the interconnected supports held fast to the table to enable precision dressing of the now upwardly exposed surfaces.
The ability to periodically dress both ends of the interconnected supports gives the user the power to continually insure that each interconnected support set is within a more exacting vertical tolerance. The machineable ends can be removed and replaced. This will enable a user to insure that all of his supports are exactly the same height by having the ability to re-dress end contact support ends upon replacement.
Replacement of the dressable ends will typically be had for long term wear, and it is contemplated that where all the supports and support sets are dressed over time that the dressing operation will result in an updated new height figure which will be taken to account by an automated system in computing the heights of the grinding spindle.
Further, the support sets can be of various unit lengths to reduce the necessity for individual vacuum line connections. For example, a work piece having a 5 foot circumference could be served by a first set of supports having a length of three feet and a second set of supports having a length of two feet.
A collection of working support sets could be employed including several three to four foot lengths, several two foot lengths and several one foot lengths. Since each working support set shares an independently actuatable upper and lower vacuum actuation possibility, each working support in each set needs to be vacuum engaged at both ends. In other words, both ends of all the supports need to be engaged between the work piece and the work table. In the given lengths of the working support sets, supports which are in excess of the numbers needed to completely support the periphery of the work piece can be aligned to extend to the vast areas within the periphery of the work piece.
As a result, the user selected limitations of the supports within a given length of the set of working supports will only be limited by a user preference on the overall weight of the set to be moved about for a new setup and the numbers of vacuum lines for which independent control of each support set is desired.
Further, and since each work piece setup typically involves pulling a vacuum about the complete periphery simultaneously, the working support sets can be serially interconnected from one working support set to another so that actuation of a single working table vacuum connection will create a working table vacuum for all working support sets, and the actuation of a single work piece vacuum connection will create a work piece vacuum for all working support sets. Thus the only limitation should be a user limitation on the number of support units within a set based purely upon handling preferences.
Finally, the most impactive aspect of the work piece support set is its simplicity of design, standardization of component parts which translates into further utilization and facilitation of maintenance. Each support contains about ten basic components, of which four are identical, resulting in only six unique components per support. The support within each set which accepts vacuum will have two additional hose tap connectors. The end supports may also include a pair of set screws to block the further transmission of vacuum where the polymeric sleeve has openings.